This project was initiated to develop a sensitive assay for measuring catechol estrogen in tissues and to study its localization, formation and actions. A sensitive and specific enzymatic assay to measure catechol estrogen in tissues has been developed. Using this assay, catechol estrogens were found to be present in brain, pituitary, liver and ovary. The enzyme that converts estrogen to catechol estrogens has been found in the brain. It is localized in the microsomes and requires cytochrome P450. This is the first microsomal P450 enzyme found in brain. Catechol estrogen blocks the stimulation of cyclic AMP in the rat hypothalamus by estrogen. BIBLIOGRAPHIC REFERENCE: Paul, S. and Skolnick, P.: Catechol estrogens inhibit oestrogen elicited accumulation of hypothalamic cyclic AMP suggesting role as endogenous anti-oestrogens. Nature 266: 559-561, 1977.